Most of the time, this output would be hidden by the next screen
update, except when editing the last line.

Shadowing core "I" is too messy. As soon as ed is loaded in memory,
nothing else that isn't "i-aware" can be loaded anymore.

I guess that's why "contexts" exist in Starting Forth, but adding
this concept just for allowing the shadowing of core words seems
overkill to me. Renaming I to i in ed seems better.

This was becoming heavy to manage.

This is the first commit I do entirely in VE. It's a habit I'm planning
on taking as it helps a lot to find usability issues.

It simplifies things. Also, removed ';' which became useless.

Previously, it would keep the old buffer displayed why typing over
it. I had kept it thus because I didn't want to erase the buffer
right away because the behavior is that when we type nothing, we
keep the buffer as-is and repeat the action.

Now, the behavior of I and F is much better. It keeps the buffer
displayed until the first non-return keystroke and then erases it.

Also, fixed PSP leak in _type and fixed PSP overuse in successful
_F (they balanced out).

Kinda proud of this one. Efficiently piggy-backing on the Block
Editor, keeping things simple, and yet, building power into the
editor.

Which are end-of-word movements.

The indicator is going to be empty most of the time and will be
emitted by the mode changer directly. That's going to the upper-right
corner and the status bar avoids emitting in that area.

Also, add MODE indirection.

Now that the boot binary is fully cross-compiled, there's no use for
the linker anymore. Theoretically, it could still be useful, but I
can't think of a real use case.

Let's take it out of the picture. If it's ever needed again, I'll
know where to find it.